Photographic printing apparatus



FIP8212 XR 199469 250.201 M1252 SREFERENC EMMINEE Feb. 13, 1934. I R. s. HOPKINS- 1,946,621

PHOTOGRAPHIC PRINTING APPARATUS Filed July 30, 1932 Patented Feb. 13, 1934 UNITED STATES PATENT OFFICE 1,946,621 PHOTOGRAPHIC PRINTING APPARATUS Application July 30, 1932. Serial No. 626,748 3 Qlaims. (Cl. 95-73) This invention relates to photography and more particularly to apparatus for accurately controlling the exposure period in photographic printing in accordance with the transparency or density of a photographic record.

One of the objects of my invention is to provide a device in which the time of exposure of a record is automatically controlled so that uniform results are always obtained. Another object is to provide an automatic exposure timing device which controls a circuit making mechanism, said mechanism comprising two movable contacts, one of which is driven at a definite angular rate and the other of which is adapted to I vary the length of the angular path of said fixed moving arm in accordance with the average transmission of the record being printed.

Other objects and advantages of my invention will appear from the following description when 20 read in connection with the accompanying drawing and its scope will be pointed out in the appended claims. i

Referring to the drawing, Fig. 1 illustrates one form which my invention may take in which the 25 radiation sensitive element receives light transmitted through both the negative and the positive. Fig. 2 is a detail of the clutch arrangement for the mechanical driven contact. Fig. 3 shows a modified form of drive for the mechanical driven contact.

In Fig. 1 my invention is shown as applied to a contact printer including two plates, and 11 of glass or other transparent material, one of which plates is movable and serves as a 35 platen for holding the sensitive material such as a sensitized paper for the print and the negative firmly in contact. A lamp 12 for furnishing a printing light is adapted to be connected to a source of supply 13 through leads 14 and 15 and 40 a switch 16. As shown, the switch 16 is held in open position by its own weight, and the momentarily closing of a push-button switch 1'7 energizes the coil 18 to close the switch 16, the closing of which energizesthe coil 19 to maintain 45 the switch 16 in.c1osed position. Operation of the switch 16 energizes the lamp 12 to start the printing exposure and the light transmitted by e the negative and positive activates the light sensitive element 20 the response of which ener- 50 gizes a meter coil 21 and its pointer 22 will assume a position corresponding to the intensity of the light falling on the light sensitive element 20.

Operation of the switch 16 to closed position mechanically actuates a clutch 23 to connect a shaft 24 to a source of motive power 25 through shaft 26, gears 2'7 and 28 to the motor shaft 29. The shaft 24 carries a mechanically driven con tact 30 and rotates it in a counter clockwise direction until it engages the meter pointer 22 to impress the potential of the battery 31 upon the grid 32 of the electronic relay 33. The relay 33 is connected to the sourceof power 13 through leads 34 and 35. The lead 34 includes a coil 36 which upon energization overcomes the holding force of the coil 19 and the switch 16 drops open.

As shown in Figs. 1 and 2 the mechanical driven contact 30 is mounted on the shaft 24. Encircling the shaft 24 is a spring 37 anchored at 38 to the frame of the apparatus and to a pin 39 in the shaft 24, this spring normally tending to bias the shaft 24 so as to hold the contact arm 30 against its stop 40.

There is a collar 41 secured on the shaft 24 by a set screw 42 and there is also a clutch element 43 mounted to slide on the shaft 24, this clutch element 43 having the usual groove 44 in which a forked end 45 of a gear shifting lever 46 is mounted. The gear shifting lever as shown consists of the forked member 45 on the end of the arm 46 of a bell crank pivoted at 4'7 the other arm 48 of which is connected to and adapted to be rocked about the pivot 4'7 by the rod 49 carried by the switch operating mechanism.

When the switch 16 is open the rod 49 through the arms 48 and 46 of the bell crank and the forked end 45 holds the clutch 23 in the position shown in Fig. 1. When the switch 16 is closed the upward movement of the rod 49 rocks the bell crank in a counter clockwise direction and moves the clutch element 43 to the right to connect the clutch engaging faces 50 and 51. The clutch face 51 is secured to the shaft 26 which is continuously rotated by any suitable means but preferably by the motor used to operate the printer in any well known manner.

In the operation of the printer the push button 1'7 is momentarily depressed to energize the coil 18 which closes the switch 16 which is then held closed by the coil 19 and the lamp 12 is energized to start the exposure. The closure of the switch 16 engaged the clutch 23 to start the mechanical driven contact 30 at a uniform angular speed in a counter clockwise direction. Simultaneously with the starting of the exposure thecell 20 is energized in accordance with the density of the negative and the meter pointer 22 assumes a position corresponding to this density. Continued movement of the contact 30 engages the needle 22 to operate the electronic relay 33 to open the switch 16 thereby stopping the exposure.

The indicating meter 21 is so adjusted that the pointer 22 is deflected toward the contact so that the greater the energization of the meter the shorter the path the contact 30 has to travel through before discontinuing the printing exposure.

The apparatus above described, with the indicating meter 21 having a deflection which is a straight line function of its energization and with the contact arm 30 rotated at a constant angular speed, will vary the time of the exposure as an approximate straight line function of the intensity of the printing light. A linear variation of the time with variation in printing light intensity will produce quite satisfactory results in most cases. However, when negatives differing greatly in density are to be printed it is found that due to what is known as the failure of the reciprocity law, prints made from very dense negatives sufier from under-exposure. This failure may be overcome by increasing the time of the exposure at a greater rate than required to maintain the above linear relation. The modification of my invention illustrated in Fig. 3 will give the desired non-linear relation.

Referring to Fig. 3 the meter pointer 22 is deflected in accordance with the response of the light sensitive cell 20 as in Fig. 1. The mechanical driven contact 30 is rotated toward the pointer 22 by the following mechanism. The contact 30 forms one arm of a bell crank, the other arm of which is provided with a curved slot 61 in which rides a roller 62. An arm 63 pivoted at 84 carries the roller 62 at one end and at its other end is provided with a segment of a gear 65 which meshes with and is adapted to be driven by a worm gear 66 mounted on the shaft 24. When the clutch 23 is engaged the shaft 24 is driven by the shaft 26 as in Fig. l and the worm gear 66 rotates the arm 63 about its pivot 64. This rotation moves the roller 62 to the left, as seen in the drawing, and due to the shape of the slot 61, the bell crank consisting of the arms 60 and 30 is rotated in a counter clockwise direction until contact is made between the contact arm 30 and the pointer 22 at which time the relay 83 is tripped and the apparatus is returned to its initial position as was the apparatus in Fig. 1. The shape of the slot 61 relative to the path of movement of the roller 62 is made such that the angular speed at which the arm 30 is rotated varies the desired amount from a uniform speed for the purpose pointed out above.

Although I have illustrated my invention as applied to a contact printer in which the exposure is controlled by turning on and off the lamp it is obviously equally applicable to a projection printer and the exposure may be controlled in any suitable manner which is well known in the art. Various modifications of my invention will readily suggest themselves to persons skilled in the art without departing from the scope of my invention as set forth in the appended claims.

What I claim as new and desire to secure by 85 Letters Patent of the United States is:

1. Photographic apparatus comprising means for supporting a sensitized layer in position to be exposed to light rays of unknown intensity and means for terminating the exposure, means movable through a path at a uniform rate from a predetermined position to a position at which the exposure terminating means is actuated, and means for varying the length of the path between said positions in accordance with the intensity of the light rays falling on said layer.

2. In photographic printing apparatus a printing light having an intensity proportional to the average transmission of a photographic record being printed, a member movable between two angularly spaced positions, driving means for moving said member at a uniform angular rate, means for simultaneously rendering said printing light effective and actuating said driving means, means operable to render said printing light ineffective after said member has moved from one to the other of said spaced positions and means for varying the angular spacing of said positions in accordance with the intensity of the printing light.

3. The combination with an electric circuit, a photographic light carried by said circuit, means for supporting a sensitized layer and a photographic negative in printing relation to said light, a circuit maker and breaker carried by said cir- 5 cuit, a continuously driven member, means normally disconnected from said member for rotating a contact member toward contacting position, means for simultaneously closing said circuit maker and connecting said means to said 20 driven member, means governed by the movement of said contacting member for opening said circuit breaker and disconnecting said driven member and said means and means for varying the path of said contact member in accordance 1 5 with the average transmission of the negative be Printed.

ROY S. HOPKINS. 

